Currently, as a fuel tank for automobiles, a fuel tank made of resin formed of high density polyethylene as the main raw material is frequently used. Thus, a connector made of synthetic resin which can be melt-bonded to the fuel tank is used for connecting the fluid path to such a fuel tank. Because such a fuel tank has its outer layer formed of high density polyethylene, the bonded portion in such a connector is also formed of polyethylene generally. However, because evaporation gas from fuel can easily pass through polyethylene, in this kind of connector, prevention of outflow of such a gas through the bonded portion as much as possible while appropriately assuring connection strength to the fuel tank is a technical problem. (Reference is made to Patent Document 1)